Protective device for electric induction furnaces



Allg. 15, 1933- T. A. FEEHAN `1,922,034

PROTECTIVE DEVICE FOR ELECTRIC INDUCTION FURNACES n Filed Nov. 23, 1931Wl' 277655 y [2n/ew for:

Patented Aug. 15, 1933 PROTECTIVE DEVICE FOR ELECTRIC I INDUCTIONFURNACES Thomas Arthur Feehan,I Trenton, N. J., assig'nor to AjaxElectrothermc Corporation, Ajax Park, N. J., a Corporation of New JerseyApplication November 23, 1931 Serial No. 576,815

2 claims. (ci. isi-26) The invention refers to protective means forinduction electric furnaces and comprises f orm-v ing a hollow spaceoutside of the melting chamber wall and inside of the energizing coil.The object is to by-pass any part of the charge which might leak throughthe furnace wall, before it has had a chance to reach the energizingcoil and cause damage.

In describing my invention I have preferred to illustrate by the use ofve figures, these being sufficient adequatelyto describevtheconstruction claimed but subject to amplification or change to meetrequired conditions.

Figures 1 and 2 show topfand section elevation views of an inductionfurnace` equipped lwith a safety device according to my invention.-

Fig. 3 is an isometric drawing showing an individual brick adapted toform, with other similar bricks, the proper spacing Cshown in Figs. 1and 2. Figs. 4 and 5 show alternate methods of lining construction whichleave a protective space according to whatis claimed.

In the usual form of lining for induction electric furnaces a protectivelining' is cemented flat against the coil. Sometimes a layer'of mica isnext applied for insulation, andflnally .a powder refractory ishard-rammed between these outer layers and a crucible or metal form.Lately it has been advocated that the rst layer of cement be substitutedby a layer of brick or even twolayers of brick with or without micabetween. Practice has also varied as to whether a crucible would be usedor Whether a lining would be sintered in place by ramming the refractorymaterial between the outer layers and a conducting sleeve which mightIbe heated to sinter the lining and then melted down to form a part ofthe firstcharge. The point brought out is that substantially all liningsthus far have been solid packed between energizing coil and charge.

Onel exception' to the above is noted in'Brace, U. S. Patent #1,823,873.In this patent a construction is claimed generally vsimilar in idea tomy-own idea but with the exception that the patentee has placed hisprotective space immediately outside of the crucible wall. Since theplacing of the space is of prime importance to my invention and sincefrom my operating experience Ihave found it important that the spacebe'as I have shown, I cnsider that the patentee in the above case inno-way anticipates my invention. I' mention it as a matter of record.

In the lining methods with which I am familiar and to which myapplication applies, great stress has been centered upon the necessityfor having charge. All crucibles are subject to crackingand wear.Instead, it is specified that granular refractory material be rammed inbehind the crucible to back up any cracksv which might form. Thisbacking material sinters enough to form a secondary crucible wall butremains granular or unsintered away from the charge. y

It is the above sintering of a granular packed mass which allows thesinter'ing of a lining in place without the use. of a crucible; theA useof a crucible even though it has initial cracks when placed, or the useof brickd inner linings or the patching and continued use of an oldlining.

The inside lining which becomes hard and sintered is `subject tocracking from expansion and contration but dependence is placed on thevbacking to remain unsintered at least for a space between coil andcharge.'

The cracking of the inside sintered Wall is of little importance whenbacked with unsintered material, as the crack cannot extend beyond thepoint where sintering stops. Hence the argument that any protectivespace left to by-pass leaking metal must eiectively be placed beyond theunsintered portion of they lining except where the crucible itself isdepended upon not to crack and where it is replaced as soon as it doescrack.

As cracks appear and are healed by sintering v of granular backingmaterial, the sintered zone gradually creeps back until the whole liningbecomes sintered. When this occurs, there is danger of metal runningthrough. Unless there is some safety device to indicate this condition,

there is a possibility that the charge making contact with the inductorcoil will cause its turns to become short circuited with afurtherpossi'- .bility ot causing a water leak and explosion before the powercan be shut oil' andthe inductor coil cleared of cooling Water.

In my invention I guard against the leaking metal coming in contact withthe coil by diverting .it toa drain at the last point in the refractorynected t an electromotive source or generat r, 2.

Capacitors, 3, are 4connectedv in parallel with the inductor coilfoi-,resonance purposes. The coil is mounted in'supporting members orframes, 4, 5.

I have preferred to show, as an example, a lining which has beensintered in place, although I 6 might as well have shown one embodying acruci ble of the pre-formed or brick masonry type.

Foundation pieces, 6, '1, are first inserted in the bottom of thefurnace. They are formed so as to leave a free space, 8, substantially`over the 10 entire bottom portion of the furnace. They may be formed togive this clearance by molding pressure points as shown in Fig. 3 or byany other suitable means. A large central hole, 9, is left, \las shown,and is covered by a thin copper disc, l5 10. Bricks, 11, are then laidclose against the coil and are luted thereto.

If preferred they may be'substituted by a solid tegrally with the brick,or in Fig. 5 where 15,

and 16 show a different method of leavingl the space using two bricks.

All brick work lining the coil is suitably of material having a lowelectrical conductivity and a high thermal conductivity. In this way thecooling effected by the cooling medium in the inductor coil istransferredto the inside brick layer ensuring a suitable temperaturegradient between outside brick wall and furnace charge.

by-pass to said discharge opening.

Refractory material, 17, is then packed around a form or crucible and issintered to form a crucible or container for the charge, 18.Anysuitable-f.

topping Cement, 19, is added t0 finish 0H the lining.

When a leak occurs in the refractory as shown at 20 the metal reachesthe space, 13, and flows down through space, 8, to -a discharge orifice,2l, and into any suitable container. 'I'he leak is quickly detected bythe operator who takes steps 35 to empty the furnace and repair thelining.

Should the metal leak through the bottom of the furnace, the disc, 10,melts letting the metal out through the orifice 9` and 21.

Having thus described my invention so that othersv skilled in the artmay be enabled to practice the same, what I desire to secure by LettersPatentis defined in what is claimed. f

1. In an induction electric furnace, an inductor coil, a Agranularpacked ref ractory lining within said coil forming a hearth, spacedbrick walls between the coil and the lining providing a bypass forleakage molten metal to prevent damage to the coil and av refractorybase beneath said lining having a discharge opening and provided 10 withpassageways leading from said by-passto said discharge opening.

' 2. In an induction electric furnace. an inductor coil, a granularpacked refractory lining within said cou forming a. hearth, spacedrefractory walls between the coil' and the lining providing a by-passfor leakage molten metal to prevent damage to the coil and a refractorybase beneath said lining having a discharge opening Y and provided withpassageways leading from said THOMAS ARTHUR FEEHAN.

lao'.

